Control cam for a valve-controlled internal combustion engine

ABSTRACT

For a peripheral cam for a valve-controlled internal-combustion engine, having a cam contour which generates at least one positive acceleration course in the valve opening area, the gas dynamics, are advantageously influenced in that the peripheral cam has an opening flank with a contour causing a delayed opening acceleration course. The opening acceleration course is generated with acceleration curves with relatively high acceleration peak values of different amounts spaced by way of an intermediate curve of relatively low positive acceleration values. A first acceleration curve has a peak value of approximately 40 to 60% of a peak value of an adjacent acceleration curve set at 100%.

BACKGROUND OF THE INVENTION

The present invention relates to an internal combustion engineperipheral cam having a cam contour, and more particularly, to a camcontour which generates at least one positive acceleration course in thevalve opening area, with an opening acceleration course which had twoacceleration curves with relatively high acceleration peak values ofdifferent amounts spaced by means of an intermediate curve of arelatively low positive acceleration.

For achieving high specific operations for a close torque, on one handand a high power on the other hand, internal-combustion engines areconventionally provided with a valve timing which has very “sharplydefined” valve lift courses for the inlet and outlet valves in order toobtain the desired flow rates by way of correspondingly rapidly changingvalve opening cross-sections. With rapidly opening outlet valves, a veryhigh exhaust lead push is therefore generated which causes a non-uniformoutflow of the exhaust gases. Since, however, the exhaust gas acousticsare very significantly influenced by the form and the amplitude of theexhaust lead push, a lead-out noise occurs in a high flow rate and ahigh opening acceleration of the outlet valve which has a highproportion of higher harmonics. This results in an intensifieddisadvantageous surface radiation of the exhaust gas system and of theinternal-combustion engine.

In known production engines with large outlet cross-sections generatedby several outlet valves per cylinder unit and high openingaccelerations produced by sharply defined valve lift courses, thisproblem was solved in that the outlet cams provided for controlling theoutlet valves per cylinder are arranged in an angularly offset mannerwith respect to one another (phasing). This arrangement which is, forexample, also described in DE-C 39 33 021 or Japanese Patent Application1-159 417 has the considerable disadvantage that each cam has to beground separately.

The high-expenditures phasing arrangement described in DE-C 195 21 141or U.S. Pat. No. 5,647,310, in the case of an outlet cam, is replaced inthat its cam contour causes an asymmetrical valve acceleration curvewith an opening acceleration curve whose maximal value is lower thanthat of the closing acceleration curve. However, such an asymmetricaloutlet valve acceleration curve is known from the book “A Decade ofContinuous Challenges” published by Honda Co. in Japan in 1993 under No.ISBN 4-9900262-0-9, from the illustrations on pages 136 and 137.

It is known that the surfaces under the closing acceleration curve andthe opening acceleration curve should be the same so that the base ofthe known opening acceleration curve having approximately 50% of themaximal value of the closing acceleration curve extends along a largerangle-of-rotation range of the cam on the abscissa. Such a widening ofthe base of the acceleration curve also exists by way of theabove-described phasing arrangement during the opening of several outletvalves of a cylinder by the superpositioning of the individual openingacceleration curves. Consequently, a predetermined widening of the base,while taking into account the above-mentioned sameness of the surfaces,causes each opening acceleration curve to be reduced in its maximalvalue for reducing an exhaust lead push.

Further, an opening acceleration course for a peripheral cam with tworelatively narrowly adjacent acceleration curves of different maximalvalues along a joint broad base is known, for example, from FIG. 38,page 85 of “Etude Dynamique de la Distribution dans les Moteurs àCombustion Interne”.

SUMMARY OF THE INVENTION

An object of the present invention is to dimension the cam contour ofthe peripheral cam at least for the valve opening area such that the gasdynamics of the internal-combustion engine on the outlet side and/or theinlet side are favorably influenced by way of the opening accelerationcourse.

This object has been achieved by providing that the first accelerationcurve has a peak value of approximately 40 to 60% of a peak value of theadjacent second acceleration curve set at 100%, and in that theascending curve section of the first acceleration curve and thedescending curve section of the second acceleration curve form at leastone projected intersection respectively with the zero acceleration lineon the abscissa, the distance between respective connection points ofthe descending curve section of the first acceleration curve and of theascending curve section of the second acceleration curve with theintermediate curve corresponding to an amount of 10 to 15% of thedistance of the abscissa intersections set at 100%.

An advantage of the present invention is an opening acceleration coursewith two acceleration curves for whose connecting intermediate curve, adimensioning range is indicated which is advantageous with respect tothe extent of the acceleration delay. Thereby, when the peripheral camdimensioned according to the present invention is used as an outlet camfor actuating an outlet valve, an exhaust lead push which is criticalwith respect to the exhaust gas acoustics is securely avoided. For aninternal-combustion engine with several outlet valves per cylinder,another advantage is that an angularly offset arrangement of the outletcams for a cylinder unit is unnecessary and therefore all outlet camscan be machined by one grinding wheel.

The opening acceleration course according to the present invention witha first acceleration curve and a second acceleration curve which ishigher than the first has, in a further embodiment of the presentinvention for an intermediate curve connecting the two accelerationcurves, a dimensioning range which is advantageous with respect to theextent of the acceleration delay.

In a further feature of the present invention, measurement ranges of thetwo acceleration curves of the opening acceleration course which havedifferent levels relate to the abscissa of an acceleration diagram. Themeasurement range or lay-out range which is relatively largerparticularly for the first acceleration curve, in conjunction with aconstant acceleration in the summit range of the first accelerationcurve and a constant acceleration of the intermediate curve betweentheir connection points by way of these steadying sections results in anacceleration delay which has an advantageously favorable effect on thegas dynamics.

This acceleration delay achieved according to the present inventioncauses on the outlet side a significant reduction of the lead-out noiseand thus of the surface radiation. On the inlet side, the openingacceleration course according to the present invention has a delay for adynamic gap formation to increase the gas velocity for whirl formation.

BRIEF DESCRIPTION OF THE DRAWING

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawingswherein:

The sole FIGURE is a diagram showing the acceleration course of thepresent invention, which acceleration course is of a type ordinarilyused in the art to describe cam contours.

DETAILED DESCRIPTION OF THE DRAWING

The starting point of the present invention is a known peripheral camfor a valve-controlled internal-combustion engine, which has a camcontour generating at least one positive acceleration course in thevalve opening area. Cam contours with high opening accelerations at highflow rates cause an exhaust lead push at outlet valves of theinternal-combustion engine whose form and amplitude results indisadvantageous exhaust gas acoustics.

In order to, in particular, avoid the higher harmonics connected withthe lead-out noise of the exhaust lead push, a delayed openingacceleration course is provided according to the present invention. Forthis purpose, the peripheral cam preferably has an opening flank with acontour by way of which an opening acceleration course 1 is generatedwhich has acceleration curves 3, 4 spaced by an intermediate curve 2 ofrelatively low positive acceleration values and having relatively highacceleration peak values a₁, a₂ of different amounts such that the firstacceleration curve 3 has a peak value a₁ of approximately 40 to 60% of apeak value a₂ of the adjacent acceleration curve 4 set at 100%.

The peripheral cam, which is preferably used as an outlet cam foractuating an outlet valve also has, with respect to its contour of theopening flank, the effect that the ascending curve section 3′ of thefirst acceleration curve 3 and the descending curve section 4″ of thesecond acceleration curve 4 form at least one projected intersection 5,6 with the zero acceleration line on the abscissa or degrees of camrotation of the acceleration diagram, in which case the distance betweenrespective connection points 7, 8 of the descending curve section 3″ ofthe first acceleration curve 3 and of the ascending curve section 4′ ofthe second acceleration curve 4 with the intermediate curve 2corresponds to an amount of 10 to 15% of the distance of the abscissaintersections 5, 6 set at 100%.

Further, the contour of the opening flank is configured such that thedistance between the first abscissa intersection 5 of the firstacceleration curve 3 and the first connection point 7 of theintermediate curve 2 to the first acceleration curve 3 corresponds to anamount of 45 to 50%, and the distance between the second connectionpoint 8 of the intermediate curve 2 and the second abscissa intersection6 of the second acceleration curve 4 corresponds to an amount of 45 to35% of the distance of the abscissa intersections 5, 6 set at 100%.

For reducing excitations in the valve gear, the first acceleration curve3 has a summit area 3′″ with a constant acceleration course. Further,the intermediate curve 2 with the constant acceleration course 2′ isconnected in front of the second higher acceleration curve 4 between theconnection points 7, 8.

In the closing range, the entire acceleration course illustrated in thesole FIGURE has a conventional closing acceleration course. Within thescope of the present invention, however, this conventional accelerationcourse can be replaced by the acceleration course 1 of the presentinvention. Further, the illustrated closing acceleration course with theopening acceleration course 1 according to the present invention canalso be used in an inlet peripheral cam for actuating an inlet valve. Inthat case, the acceleration delay according to the present inventionadvantageously generates a dynamic valve gap for triggering a whirlformation. In addition, the mixture formation can also be influencedadvantageously.

The invention is preferably used in multi-valve engines, particularly infour-valve engines.

What is claimed is:
 1. Peripheral cam for a valve-controlledinternal-combustion engine, comprising an opening flank with a camcontour configured to generate at least one positive acceleration coursein a valve opening area, with an opening acceleration course havingfirst and second acceleration curves with acceleration peak values ofdifferent amounts spaced by way of an intermediate curve of positiveacceleration lower than the first and second acceleration curves,wherein the first acceleration curve has a peak value of approximately40 to 60% of a peak value of the adjacent second acceleration curve setat 100%, an ascending curve section of the first acceleration curve anda descending curve section of the second acceleration curve eachrespectively intersecting with a zero acceleration line, and a distancebetween respective connection points of the descending curve section ofthe first acceleration curve and of the ascending curve section of thesecond acceleration curve with the intermediate curve corresponding toan amount of about 10 to 15% of the distance between the intersectionsat the zero acceleration line of the first and second accelerationcurves.
 2. Peripheral cam according to claim 1, wherein a contour of theopening flank is also configured such that a distance between a firstintersection of the at least one intersection and the first projectedconnection point of the intermediate curve corresponds to an amount ofabout 45 to 50%, and a distance between the second projected connectionpoint of the intermediate curve and the second intersection correspondsto an amount of about 45 to 35% of the distance between theintersections of the first and second acceleration curves at the zeroacceleration line.
 3. Peripheral cam according to claim 1, wherein thefirst acceleration curve has a summit area with a constant accelerationcourse.
 4. Peripheral cam according to claim 3, wherein a contour of theopening flank also is configured such that a distance between a firstintersection of the at least one intersection and the first projectedconnection point of the intermediate curve corresponds to an amount ofabout 45 to 50%, and a distance between the second projected connectionpoint of the intermediate curve and the second intersection correspondsto an amount of about 45 to 35% of the distance between theintersections of the first and second acceleration curves at the zeroacceleration line.
 5. Peripheral cam according to claim 1, wherein theintermediate curve in sections between the connection points has aconstant acceleration course.
 6. Peripheral cam according to claim 5,wherein a contour of the opening flank also is configured such that adistance between first intersection of the at least one intersection andthe first projected connection point of the intermediate curvecorresponds to an amount of about 45 to 50%, and a distance between thesecond projected connection point of the intermediate curve and thesecond intersection corresponds to an amount of about 45 to 35% of thedistance between the intersections of the first and second accelerationcurves at the zero acceleration line.
 7. Peripheral cam according toclaim 6, wherein the first acceleration curve has a summit area with aconstant acceleration course.
 8. Peripheral cam according to claim 7,wherein a contour of the opening flank is configured such that adistance between a first intersection of the at least one intersectionand the first projected connection point of the intermediate curvecorresponds to an amount of about 45 to 50%, and a distance between thesecond projected connection point of the intermediate curve and thesecond intersection corresponds to an amount of about 45 to 35% of thedistance between the intersections of the first and second accelerationcurves at the zero acceleration line.
 9. Method of using a peripheralcam, comprising an opening flank of the peripheral cam having a camcontour configured to generate at least one positive acceleration coursein a valve opening area, with an opening acceleration course havingfirst and second acceleration curves with acceleration peak values ofdifferent amounts spaced by way of an intermediate curve of positiveacceleration lower than the first and second acceleration curve whereinthe first acceleration curve has a peak value of approximately 40 to 60%of a peak value of the adjacent second acceleration curve set at 100%,an ascending curve section of the first acceleration curve and adescending curve section of the second acceleration curve eachrespectively intersecting with a zero acceleration line, and a distancebetween respective connection points of the descending curve section ofthe first acceleration curve and of the ascending curve section of thesecond acceleration curve with the intermediate curve corresponding toan amount of about 10 to 15% of the distance between the intersectionsof the first and second acceleration curves at the zero accelerationline, comprising the step of using the peripheral cam as a cam foractuating one of an inlet valve and an outlet valve.
 10. Method of usinga peripheral cam according to claim 9, wherein the first accelerationcurve has a summit area with a constant acceleration course.
 11. Methodof using a peripheral cam according to claim 10, wherein a contour ofthe opening flank is configured such that a distance between a firstintersection of the at least one intersection and the first projectedconnection point of the intermediate curve corresponds to an amount ofabout 45 to 50%, and a distance between the second projected connectionpoint of the intermediate curve and the second intersection correspondsto an amount of about 45 to 35% of the distance of the betweenintersections of the first and second acceleration curves at the zeroacceleration line.
 12. Method of using a peripheral cam according toclaim 11, wherein the intermediate curve in sections between theconnection points has a constant acceleration course.